D-amino acid oxidase ("DAO") is a flavoprotein known to be able to convert cephalosporin C ("Ceph C") to .alpha.-ketoadipyl cephalosporanic acid (".alpha.-ketoadipyl 7-ACA), hydrogen peroxide, and ammonia. .alpha.-ketoadipyl 7-ACA, upon reaction with hydrogen peroxide, can be further transformed into glutaryl-7-aminocephalosporanic acid ("GL-7-ACA"). Since GL-7-ACA is a starting material for the production of cephem antibiotics, DAO is of great industrial interest.
Besides the production of .alpha.-keto acids (Tosa et al., Agric Biol Chem 1974! 38, 1529-1536), DAO has been used in the resolution of racemic mixtures of amino acids (Tu et al., Separation Sci 1972! 7, 403-408) and analytical determination of amino acids (Guilbault et al., Anal Chim Acta 1971! 56, 285-290). DAO can be found in various microorganisms, insects and animals.